// Copyright 2009 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package Scanner

export EOF;
const (
	ILLEGAL = iota;
	EOF;
	IDENT;
	STRING;
	NUMBER;

	COMMA;
	COLON;
	SEMICOLON;
	PERIOD;

	LPAREN;
	RPAREN;
	LBRACK;
	RBRACK;
	LBRACE;
	RBRACE;
	
	ASSIGN;
	DEFINE;
	
	INC;
	DEC;
	NOT;
	
	AND;
	OR;
	XOR;
	
	ADD;
	SUB;
	MUL;
	QUO;
	REM;
	
	EQL;
	NEQ;
	LSS;
	LEQ;
	GTR;
	GEQ;

	SHL;
	SHR;

	ADD_ASSIGN;
	SUB_ASSIGN;
	MUL_ASSIGN;
	QUO_ASSIGN;
	REM_ASSIGN;

	AND_ASSIGN;
	OR_ASSIGN;
	XOR_ASSIGN;
	
	SHL_ASSIGN;
	SHR_ASSIGN;

	CAND;
	COR;
	
	// keywords
	KEYWORDS_BEG;
	BREAK;
	CASE;
	CONST;
	CONTINUE;
	DEFAULT;
	ELSE;
	EXPORT;
	FALLTHROUGH;
	FALSE;
	FOR;
	FUNC;
	GO;
	GOTO;
	IF;
	IMPORT;
	INTERFACE;
	MAP;
	NEW;
	NIL;
	PACKAGE;
	RANGE;
	RETURN;
	SELECT;
	STRUCT;
	SWITCH;
	TRUE;
	TYPE;
	VAR;
	KEYWORDS_END;
)


var Keywords *map [string] int;


export TokenName
func TokenName(tok int) string {
	switch (tok) {
	case ILLEGAL: return "illegal";
	case EOF: return "eof";
	case IDENT: return "ident";
	case STRING: return "string";
	case NUMBER: return "number";

	case COMMA: return ",";
	case COLON: return ":";
	case SEMICOLON: return ";";
	case PERIOD: return ".";

	case LPAREN: return "(";
	case RPAREN: return ")";
	case LBRACK: return "[";
	case RBRACK: return "]";
	case LBRACE: return "{";
	case RBRACE: return "}";

	case ASSIGN: return "=";
	case DEFINE: return ":=";
	
	case INC: return "++";
	case DEC: return "--";
	case NOT: return "!";

	case AND: return "&";
	case OR: return "|";
	case XOR: return "^";
	
	case ADD: return "+";
	case SUB: return "-";
	case MUL: return "*";
	case QUO: return "/";
	case REM: return "%";
	
	case EQL: return "==";
	case NEQ: return "!=";
	case LSS: return "<";
	case LEQ: return "<=";
	case GTR: return ">";
	case GEQ: return ">=";

	case SHL: return "<<";
	case SHR: return ">>";

	case ADD_ASSIGN: return "+=";
	case SUB_ASSIGN: return "-=";
	case MUL_ASSIGN: return "+=";
	case QUO_ASSIGN: return "/=";
	case REM_ASSIGN: return "%=";

	case AND_ASSIGN: return "&=";
	case OR_ASSIGN: return "|=";
	case XOR_ASSIGN: return "^=";

	case SHL_ASSIGN: return "<<=";
	case SHR_ASSIGN: return ">>=";

	case CAND: return "&&";
	case COR: return "||";

	case BREAK: return "break";
	case CASE: return "case";
	case CONST: return "const";
	case CONTINUE: return "continue";
	case DEFAULT: return "default";
	case ELSE: return "else";
	case EXPORT: return "export";
	case FALLTHROUGH: return "fallthrough";
	case FALSE: return "false";
	case FOR: return "for";
	case FUNC: return "func";
	case GO: return "go";
	case GOTO: return "goto";
	case IF: return "if";
	case IMPORT: return "import";
	case INTERFACE: return "interface";
	case MAP: return "map";
	case NEW: return "new";
	case NIL: return "nil";
	case PACKAGE: return "package";
	case RANGE: return "range";
	case RETURN: return "return";
	case SELECT: return "select";
	case STRUCT: return "struct";
	case SWITCH: return "switch";
	case TRUE: return "true";
	case TYPE: return "type";
	case VAR: return "var";
	}
	
	return "???";
}


func is_whitespace (ch int) bool {
	return ch == ' ' || ch == '\r' || ch == '\n' || ch == '\t';
}


func is_letter (ch int) bool {
	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= 128 ;
}


func digit_val (ch int) int {
	if '0' <= ch && ch <= '9' {
		return ch - '0';
	}
	if 'a' <= ch && ch <= 'f' {
		return ch - 'a' + 10;
	}
	if 'A' <= ch && ch <= 'F' {
		return ch - 'A' + 10;
	}
	return 16;  // larger than any legal digit val
}


export Scanner
type Scanner struct {
	src string;
	pos int;
	ch int;  // one char look-ahead
}


export Token
type Token struct {
	val int;
	beg, end int;
	txt string;
}


func (T *Token) Print () {
	print TokenName(T.val), " [", T.beg, ", ", T.end, "[ ", T.txt, "\n";
}


// Read the next Unicode char into S.ch.
// S.ch < 0 means end-of-file.
//
func (S *Scanner) Next () {
	const (
		Bit1 = 7;
		Bitx = 6;
		Bit2 = 5;
		Bit3 = 4;
		Bit4 = 3;

		// TODO 6g constant evaluation incomplete
		T1 = 0x00;  // (1 << (Bit1 + 1) - 1) ^ 0xFF;  // 0000 0000
		Tx = 0x80;  // (1 << (Bitx + 1) - 1) ^ 0xFF;  // 1000 0000
		T2 = 0xC0;  // (1 << (Bit2 + 1) - 1) ^ 0xFF;  // 1100 0000
		T3 = 0xE0;  // (1 << (Bit3 + 1) - 1) ^ 0xFF;  // 1110 0000
		T4 = 0xF0;  // (1 << (Bit4 + 1) - 1) ^ 0xFF;  // 1111 0000

		Rune1 = 1 << (Bit1 + 0*Bitx) - 1;  // 0000 0000 0111 1111
		Rune2 = 1 << (Bit2 + 1*Bitx) - 1;  // 0000 0111 1111 1111
		Rune3 = 1 << (Bit3 + 2*Bitx) - 1;  // 1111 1111 1111 1111

		Maskx = 0x3F;  // 1 << Bitx - 1;  // 0011 1111
		Testx = 0xC0;  // Maskx ^ 0xFF;  // 1100 0000

		Bad	= 0xFFFD;  // Runeerror
	);

	src := S.src;  // TODO only needed because of 6g bug
	lim := len(src);
	pos := S.pos;
	
	// 1-byte sequence
	// 0000-007F => T1
	if pos >= lim {
		S.ch = -1;  // end of file
		return;
	}
	c0 := int(src[pos]);
	pos++;
	if c0 < Tx {
		S.ch = c0;
		S.pos = pos;
		return;
	}

	// 2-byte sequence
	// 0080-07FF => T2 Tx
	if pos >= lim {
		goto bad;
	}
	c1 := int(src[pos]) ^ Tx;
	pos++;
	if c1 & Testx != 0 {
		goto bad;
	}
	if c0 < T3 {
		if c0 < T2 {
			goto bad;
		}
		r := (c0 << Bitx | c1) & Rune2;
		if  r <= Rune1 {
			goto bad;
		}
		S.ch = r;
		S.pos = pos;
		return;
	}

	// 3-byte sequence
	// 0800-FFFF => T3 Tx Tx
	if pos >= lim {
		goto bad;
	}
	c2 := int(src[pos]) ^ Tx;
	pos++;
	if c2 & Testx != 0 {
		goto bad;
	}
	if c0 < T4 {
		r := (((c0 << Bitx | c1) << Bitx) | c2) & Rune3;
		if r <= Rune2 {
			goto bad;
		}
		S.ch = r;
		S.pos = pos;
		return;
	}

	// bad encoding
bad:
	S.ch = Bad;
	S.pos += 1;
	return;
}


func Init () {
	Keywords = new(map [string] int);
	
	for i := KEYWORDS_BEG; i <= KEYWORDS_END; i++ {
	  Keywords[TokenName(i)] = i;
	}
}


func (S *Scanner) Open (src string) {
	if Keywords == nil {
		Init();
	}

	S.src = src;
	S.pos = 0;
	S.Next();
}


func (S *Scanner) Expect (ch int) {
	if S.ch != ch {
		panic "expected ", string(ch), " found ", string(S.ch);
	}
	S.Next();
}


func (S *Scanner) SkipWhitespace () {
	for is_whitespace(S.ch) {
		S.Next();
	}
}


func (S *Scanner) SkipComment () {
	if S.ch == '/' {
		// comment
		S.Next();
		for S.ch != '\n' && S.ch >= 0 {
			S.Next();
		}
		
	} else {
		/* comment */
		S.Next();
		for S.ch >= 0 {
			ch := S.ch;
			S.Next();
			if ch == '*' && S.ch == '/' {
				S.Next();
				return;
			}
		}
		panic "comment not terminated";
	}
}


func (S *Scanner) ScanIdentifier () int {
	beg := S.pos - 1;
	for is_letter(S.ch) || digit_val(S.ch) < 10 {
		S.Next();
	}
	end := S.pos - 1;
	
	var tok int;
	var present bool;
	tok, present = Keywords[S.src[beg : end]];
	if !present {
		tok = IDENT;
	}
	
	return tok;
}


func (S *Scanner) ScanMantissa (base int) {
	for digit_val(S.ch) < base {
		S.Next();
	}
}


func (S *Scanner) ScanNumber (seen_decimal_point bool) int {
	if seen_decimal_point {
		S.ScanMantissa(10);
		goto exponent;
	}
	
	if S.ch == '0' {
		// TODO bug: doesn't accept 09.0 !
		// int
		S.Next();
		if S.ch == 'x' || S.ch == 'X' {
			// hexadecimal int
			S.Next();
			S.ScanMantissa(16);
		} else {
			// octal int
			S.ScanMantissa(8);
		}
		return NUMBER;
	}
	
	// decimal int or float
	S.ScanMantissa(10);
	
	if S.ch == '.' {
		// float
		S.Next();
		S.ScanMantissa(10)
	}
	
exponent:
	if S.ch == 'e' || S.ch == 'E' {
		// float
		S.Next();
		if S.ch == '-' || S.ch == '+' {
			S.Next();
		}
		S.ScanMantissa(10);
	}
	return NUMBER;
}


func (S *Scanner) ScanDigits(n int, base int) {
	for digit_val(S.ch) < base {
		S.Next();
		n--;
	}
	if n > 0 {
		panic "illegal char escape";
	}
}


func (S *Scanner) ScanEscape () string {
	// TODO: fix this routine
	
	ch := S.ch;
	S.Next();
	switch (ch) {
	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', '\'', '"':
		return string(ch);
		
	case '0', '1', '2', '3', '4', '5', '6', '7':
		S.ScanDigits(3 - 1, 8);  // 1 char already read
		return "";  // TODO fix this
		
	case 'x':
		S.ScanDigits(2, 16);
		return "";  // TODO fix this
		
	case 'u':
		S.ScanDigits(4, 16);
		return "";  // TODO fix this

	case 'U':
		S.ScanDigits(8, 16);
		return "";  // TODO fix this

	default:
		panic "illegal char escape";
	}
}


func (S *Scanner) ScanChar () int {
	// '\'' already consumed

	ch := S.ch;
	S.Next();
	if ch == '\\' {
		S.ScanEscape();
	}

	S.Expect('\'');
	return NUMBER;
}


func (S *Scanner) ScanString () int {
	// '"' already consumed

	for S.ch != '"' {
		ch := S.ch;
		S.Next();
		if ch == '\n' || ch < 0 {
			panic "string not terminated";
		}
		if ch == '\\' {
			S.ScanEscape();
		}
	}

	S.Next();
	return STRING;
}


func (S *Scanner) ScanRawString () int {
	// '`' already consumed

	for S.ch != '`' {
		ch := S.ch;
		S.Next();
		if ch == '\n' || ch < 0 {
			panic "string not terminated";
		}
	}

	S.Next();
	return STRING;
}


func (S *Scanner) Select2 (tok0, tok1 int) int {
	if S.ch == '=' {
		S.Next();
		return tok1;
	}
	return tok0;
}


func (S *Scanner) Select3 (tok0, tok1, ch2, tok2 int) int {
	if S.ch == '=' {
		S.Next();
		return tok1;
	}
	if S.ch == ch2 {
		S.Next();
		return tok2;
	}
	return tok0;
}


func (S *Scanner) Select4 (tok0, tok1, ch2, tok2, tok3 int) int {
	if S.ch == '=' {
		S.Next();
		return tok1;
	}
	if S.ch == ch2 {
		S.Next();
		if S.ch == '=' {
			S.Next();
			return tok3;
		}
		return tok2;
	}
	return tok0;
}


func (S *Scanner) Scan (t *Token) (tok, beg, end int) {
	S.SkipWhitespace();
	
	var tok int = ILLEGAL;
	var beg int = S.pos - 1;
	var end int = beg;
	
	ch := S.ch;
	switch {
	case is_letter(ch): tok = S.ScanIdentifier();
	case digit_val(ch) < 10: tok = S.ScanNumber(false);
	default:
		S.Next();
		switch ch {
		case -1: tok = EOF;
		case '"': tok = S.ScanString();
		case '\'': tok = S.ScanChar();
		case '`': tok = S.ScanRawString();
		case ':': tok = S.Select2(COLON, DEFINE);
		case '.':
			if digit_val(S.ch) < 10 {
				tok = S.ScanNumber(true);
			} else {
				tok = PERIOD;
			}
		case ',': tok = COMMA;
		case ';': tok = SEMICOLON;
		case '(': tok = LPAREN;
		case ')': tok = RPAREN;
		case '[': tok = LBRACK;
		case ']': tok = RBRACK;
		case '{': tok = LBRACE;
		case '}': tok = RBRACE;
		case '+': tok = S.Select3(ADD, ADD_ASSIGN, '+', INC);
		case '-': tok = S.Select3(SUB, SUB_ASSIGN, '-', DEC);
		case '*': tok = S.Select2(MUL, MUL_ASSIGN);
		case '/':
			if S.ch == '/' || S.ch == '*' {
				S.SkipComment();
				// cannot simply return because of 6g bug
				tok, beg, end = S.Scan(t);
				return tok, beg, end;
			}
			tok = S.Select2(QUO, QUO_ASSIGN);
		case '%': tok = S.Select2(REM, REM_ASSIGN);
		case '^': tok = S.Select2(XOR, XOR_ASSIGN);
		case '<': tok = S.Select4(LSS, LEQ, '<', SHL, SHL_ASSIGN);
		case '>': tok = S.Select4(GTR, GEQ, '>', SHR, SHR_ASSIGN);
		case '=': tok = S.Select2(ASSIGN, EQL);
		case '!': tok = S.Select2(NOT, NEQ);
		case '&': tok = S.Select3(AND, AND_ASSIGN, '&', CAND);
		case '|': tok = S.Select3(OR, OR_ASSIGN, '|', COR);
		default: tok = ILLEGAL;
		}
	}
	
	end = S.pos - 1;
	
	t.val = tok;
	t.beg = beg;
	t.end = end;
	t.txt = S.src[beg : end];
	
	return tok, beg, end;
}